This invention relates to rivets and particularly to the type that is flared plus the construction thereof.
The problem solved by this invention is best understood by referring to FIG. 1 which shows a typical, commercially available flared tubular rivet. As noted the rivet 10 after installed in the pieces to be secured is flared at the end 12 opposite the rivet head 14. The following disadvantages are evidenced when this method of riveting is employed:
(1) The flared end must be upset by either impacting or pressing the tubular end putting the rivet shank 16 in compression during assembly. When tool pressure is released, the rivet shank 16 springs back resulting in a loose fit under the rivet head; PA1 (2) The flaring process requires special tooling and experience has shown that, even with production tooling uniform flaring is difficult to achieve; and PA1 (3) By virtue of the compression forces the shank 16 occasionally buckles.
I have found that I can obviate the above referred to disadvantages by designing the rivet to carry the swaging mechanism. A grasping handle or stem extending from the externally accessible swaging mechanism of the rivet is pulled to effectuate the flaring of the end by withdrawing of the swaging mechanism. In one embodiment, it is contemplated that the end of the piece being secured is contoured to allow the shear wedge of the rivet to be flared a sufficient distance to hold the rivet in its securing position while retaining the swaging mechanism. It is contemplated that the working stem breaks off while the swaging mechanism is pulled. It is also contemplated that the contouring is such that the swaging mechanism can be completely withdrawn. In both types, the pulling of the swaging mechanism loads the head of the rivet against the face of the member to be secured, thus assuring that the entire rivet is in tension. The purpose of designing the swaging mechanism to remain in the rivet after flaring is to enhance its tension capability. If this tension capacity is not required the rivet can be designed so that the swaging mechanism can be completely removed.
Some of the advantages that are afforded by this invention are listed hereinbelow, but are not limited thereto:
(1) Prevents looseness under manufactured head as experienced with present flared rivets. The rivet shank is put in tension when the stem is pulled to form the flare providing a tight fit under the manufactured head.
(2) Increases tension capability. With the head of the stem remaining in the flared end of the rivet, the "shear wedge" prevents the rivet from pulling out. The tension capability is now determined by shear strength of "shear wedge" and the tensile strength in the tubular portion of the rivet rather than the strength of the flare itself.
(3) Eases and enhances repeatability of the installation. Self-flaring rivet can be made to be compatible with hand upsetting guns used for blind rivets. This eliminates the need for the much more complex and expensive tooling used to upset present flared rivets. This also facilitates assembly in the field. All the features required to flare the rivet properly are built into the rivet itself. Thus, there is no dependence on the skill of the mechanic for proper installation, which should result in significant cost savings.
(4) The self-flaring rivet is not length limited since all the flaring features are contained in the flared end. Standard blind rivets require that the entire length of the shank be drilled to accommodate the stem which is impractical in long lengths.
(5) The self-flaring rivet has a wide variety of shear pin applications. The rivet shank can be a high strength heat treated material with the flared end locally annealed, or, in a two-piece design, the shank can be high strength and the flare end soft.